The present invention relates to a synchronous machine of the kind set forth below.
The large majority of such synchronous machines are rotary machines, the rotor of which is normally cylindrical. Accordingly, the invention will be described primarily with reference to such machines. It will be understood, however, that the invention can also be applied to rotary machines which are equipped with rotors of other configurations, for instance disc-like rotors or conical rotors, and also to linear machines.
According to conventional techniques, it is customary in a synchronous machine, the armature winding of which shall have a sinusoidal terminal or line voltage, or, in the case of a motor, is supplied with a sinusoidal terminal current, to design the armature winding, which is normally mounted on the stator of the machine, and the field magnet system, which is normally mounted on the rotor, such that the density of the flux which exists in the air gap between the stator and the rotor, and which is linked with the armature winding, is distributed sinusoidally as seen along the direction of movement of the two relatively movable parts of the machine, i.e. over the circumference in the case of a conventional rotary machine. This applies irrespective of whether the field system comprises salient field poles provided with permanent magnets or electromagnetic field coils, or comprises a distributed field winding mounted on a ferromagnetic iron core, for instance on a cylindrical rotor core. In the case of machines provided with salient field poles, it is sometimes possible to tolerate some deviation from the desired sinusoidal distribution of the air-gap flux-density, namely such deviations as those caused by deviations in the shape of the permanent magnets or the pole shoes from the theoretically ideal shape, which substantially simplify the manufacture of the permanent magnets or the pole shoes.